1. Technical Field
This invention relates to a label transfer device for stripping labels from a label tape prior to placement upon a product, and more particularly to a label transfer device wherein the label tape is held in a fixed position, a movable transfer arm is positioned and attaches to the label prior to its being removed from the label tape, and the stripping plate moves instead of the label tape as the label is stripped from the tape.
2. Background Art
In today's commercial labeling applications, labels are typically provided in rolls, wherein the individual labels are pre-printed on one surface and provided with an adhesive on the opposite surface. The labels are pre-positioned on a label tape, ribbon, or webbing, sometimes called a release liner, for example, waxed paper ribbon, to which the label will adhere with a relatively low adhesive force so that the label can be easily peeled from the ribbon prior to placement on a package or product. Typically, the label material is paper or a plastic such as nylon, polypropylene, polyester or a polyamide, the label tape or ribbon is waxed paper or plastic and the adhesive is selected for its adhesion characteristics both for holding on the product or packaging and for a relatively low adhesion to the release liner or label tape.
Labels are peeled from the release liner or label tape by use of a process which is common to any type of label removal, whether it be by machine or by hand. In the consumer market, blank labels usually accompany blank, unrecorded audio or video tape cassettes. These labels are initially affixed to a label tape or backing which has a waxed or plastic surface. In order to remove the label, the backing is bent away from the more rigid label so as to form a small radius shear line between the rigid label and the more pliable backing. The label can then be peeled off along the shear line by pulling the backing and the label away from each other.
In commercial applications, the same concept is used to remove labels from a release liner or label tape. FIGS. 1A and 1B demonstrate the prior art process in conceptual format. In FIG. 1A there is shown a flat stripping plate and stripping roller. The labels and tape are passed over the top surface of the stripping plate and then over and around a stripping edge of the stripping plate and then around the stripping roller. The label, being relatively rigid, or inflexible, is attached to the more flexible label tape. The adhesive force of the glue on the label, holding the label to the tape, is less than the force necessary to bend the rigid label around the stripping edge radius, and as a result the label, as shown in FIG. 1A, peels off extending out from the stripping plate as the more pliable label tape bends around the stripping edge of the stripping plate, thereby separating the label from the label tape.
The problem is that the label, although being fairly rigid, is still flexible, and in the case of long, thin labels, for example, uniform product bar code labels, will bend or twist under their own weight as they are stripped off of the label tape as is shown in FIG. 1B.
A pick up head or transfer device, typically a pick up head which draws a vacuum to suck and hold the label up against a vacuum screen, is provided to capture the label as it is being stripped off the label tape. The vacuum head is typically part of a mechanical system which, and once it has captured the label, is used to reposition it for placement upon the product or packaging.
The prior art can generally be described as having all of its mechanical pieces stationary relative to each other with a moving label tape which passes over the stationary stripping plate, down around the stripping edge with the labels being stripped off and extending out away from the tape into a position where, hopefully, they can be captured by the vacuum head. It is not the most reliable of systems, especially if it is being used in conjunction with bar code labels which are long, thin and flexible. There will be vacuum head capture misses which will result in label skips unless the production line is temporarily shut down to correct the problem.
To minimize these problems, the prior art has normally oriented the stripping plate such that there is a gravity assist to the free swinging labels that are being stripped off the tape. As a result, a label is vertically oriented at the time that the vacuum head attaches itself to the label, thus requiring the mechanical or robotic arm to rotate from a vertical orientation to capture the label, to a horizontal orientation for placement of the label on a horizontally oriented product or package surface.
Another problem with the prior art, particularly with long, thin labels, such as bar code labels, is label curling as the label is being stripped from the webbing or tape. This is shown in prior art FIG. 1B. To minimize curling, prior art labels are thicker than would necessarily be required if they could be removed from the label tape without curling. Thinner labels are less expensive, and as a general rule, there is a trade off in the prior art between the curling of thinner labels and the expense of thicker labels. This usually results in a compromise wherein some pickup and placement misses due to label curling are permitted to occur in order to save the expense of the more expensive, thicker and stiffer labels.
Another problem with the prior art is that every label must be stripped from the label tape and picked up by the vacuum head. Ideally a label transfer machine such as disclosed in the present invention is capable of sensing defective labels and skipping them, allowing them to remain on the scrap label tape.
Accordingly, what is needed is a label transfer device wherein the pick up head positively attaches to the label prior to its being stripped from the label tape so as to eliminate curling and bending of stripped labels as the label tape passes over and bends around the stripping edge of the stripping plate, thus enabling the use of thinner, more flexible labels. Another object of the present invention is a positive attachment between the vacuum head and the label prior to its being stripped such that the stripping action is not gravity dependent, but rather can be accomplished in any orientation, including upside down, wherein the label is stripped from underneath the label tape, so that the placement or robotic mechanism need not always operate in both a vertical and horizontal orientation.
Another object of the present invention is to provide a sensor capable of sensing defective labels and a control mechanism for skipping them on the tape, allowing them to remain with the scrap label tape. A final object of the present invention is to provide a vacuum head pick up of the label prior to its being stripped from the label tape so that the pickup is more accurate, resulting in more accurate label placement on the product or packaging materials.